Title Response of osmotic adjustment and seed yield in Brassica to water deficit at different growth stages Description Research Update for Growers - Western Region - February 2004 GRDC Project Authors Presented UWA368 Q. Ma and D.W. Turner, School of Plant Biology, Faculty of Natural and Agricultural Sciences, UWA, Crawley WA 6009 S.R. Niknam, Victoria Institute for Dryland Agriculture, Horsham VIC 3401 Paper reviewed by: Dr Janet Wroth Perth, WA Note - this report may contain independently supported projects, which complement the work in this GRDC research program. Take home messages Canola (Brassica napus L.) is a major rotation crop but low yield has limited its adoption by farmers in the water-limited regions of southern Australia, where drought events can occur at any stages of crop development. However, little is known about osmotic adjustment (OA, a physiological mechanism for drought tolerance) over the growth stages and its association with yield sensitivity. At the early growth stages, all tested genotypes expressed OA when they experienced a single water deficit that was not severe enough to reduce plant growth or seed yield. Genotypes that experienced a single cycle of water deficit at anthesis and maintained OA (albeit little at seed filling) showed much less yield reduction than those with little OA at anthesis. The study suggests that yield sensitivity of Brassica oilseeds to water deficit at late growth stages can be modified by the physiological trait of OA. Aims This study examined the effects of a single cycle of soil water deficit at different growth stages on OA, seed yield and yield components in Brassica oilseeds. Method Expt 1 was conducted under glasshouse conditions of 18 C day and 13 C night during late summer and autumn, and canola cv. Monty (Brassica napus) and mustard line 397-23-2-3-3 (B. juncea) were grown in potting mix in free-draining 8-L pots. Expt 2 was conducted at Merredin Dryland Research Institute in the
2003 season. Canola cultivars Monty and Karoo and mustard line JN25 were grown from late May to early November and at sowing 100 kg/ha of Agran (16.8% N, 10% P, 14.2% S, 0.1% Ca and 0.06% Zn) were applied plus 80 kg/ha of urea 6 weeks later. In glasshouse experiment, the 2 genotypes were well-watered (WW) throughout plant development or subjected to single water deficit () by withholding water at 4 stages: juvenile (4 fully-expanded leaves), stem elongation, anthesis or seedfill. The duration of withholding water was 14 days at juvenile, 9 days each at stem elongation and anthesis, and 8 days at seed-fill. In the field, the 3 genotypes were rain-fed till anthesis and then divided into 2 groups, one continuously rainfed and the other drip-irrigated weekly until plant maturity. The quantity of irrigation was based on the amount of a local Class A pan evaporation minus the rainfall at the same period. Measurements of leaf relative water content, osmotic potential and OA were described in our other paper in this volume (Ma et al. 2004). Seed yield, yield components and harvest index were measured at the final harvest. The effects of water deficit on individual genotypes were estimated using the ratio of to WW plant in the glasshouse and the ratio of rain-fed to irrigated treatment in the field. This removed the inherent differences in yield potential between the genotypes. Results Both canola cv. Monty and mustard line 397-23-2-3-3 expressed OA at juvenile and elongation stages (Table 1). In comparison, OA was maintained in the mustard line but not in the canola cultivar at anthesis, and there was little OA in either genotype at seed-fill stage. The mustard plants produced twice as many pods but only half of the seed number per pod as did the canola plants. Single water deficit at juvenile or elongation stage had a stimulating effect on pod number in both genotypes. Water deficit at anthesis or seed-fill significantly reduced pod number and/or seed number per pod, seed yield and harvest index in canola but not in mustard (Table 2). In the field, cv. Monty showed low OA at anthesis and had 30% yield reduction under rain-fed conditions compared with the irrigated plants, while the osmotically-adjusting cvs Karoo and mustard line JN25 had about 10% yield reduction (Table 3). The yield reduction in cv. Monty was largely due to the reduction of total seed number and harvest index. Conclusion This study found that the magnitude of leaf OA in Brassica oilseeds changed with plant development and genotypes adjusting osmotically at anthesis had much less yield reduction than genotypes with little adjustment under drought. The finding was consistent with our previous field trials at a low rainfall site, where leaf OA was also measured around anthesis (Niknam et al. 2003). In Brassica oilseeds, water supply is critical during flowering and early pod development when
numbers of pods and seeds are being determined (Richards and Thurling 1978). We believe that OA expression during that time would play an active role in drought tolerance to maintain yields. Table 1. Leaf osmotic adjustment (MPa) of canola cvs Monty and Karoo, and mustard lines 397-23-2-3- 3 and JN25 under glasshouse and field conditions Glasshouse experiment Juvenile Elongation Anthesis Seed-fill Monty 0.21 0.53 0.04 0.02 397-23-2-3-3 0.25 0.32 0.29 0.03 Field experiment Monty 0.14 0.04 Karoo 0.48 0.07 JN25 0.42 0.02 The difference of osmotic adjustment from zero is determined by t test (P = 0.05), where t = OA/se and se is the standard error of OA. Table 2. Seed yield and yield components of well-watered plants (WW), and plants subjected to a single water deficit () at juvenile (S1), elongation (S2), anthesis (S3) or seed-fill (S4) stages Pods/plant Seeds/pod 100 seed wt (g) Canola cv. Monty Seed wt (g)/plant Total dry wt. (g)/plant Harvest index WW 390.0 a 15.3 a 0.351 a 20.74 ab 70.10 ab 0.29 a (S1) (S2) (S3) (S4) 456.7 a 15.1 a 0.342 a 23.40 a 76.60 a 0.30 a 377.0 ab 13.9 ab 0.356 a 18.31 bc 68.59 b 0.27 a 329.3 b 12.7 b 0.364 a 15.02 c 64.49 b 0.23 b 384.0 ab 11.4 b 0.353 a 15.31 c 67.62 ab 0.22 b Mustard line 397-23-2-3-3 WW 777.7 ab 7.3 a 0.325 a 18.46 a 76.19 ab 0.24 a (S1) (S2) 848.7 a 7.7 a 0.324 a 20.67 a 84.96 a 0.28 a 694.3 ab 8.4 a 0.312 a 18.18 a 71.18 ab 0.26 a
(S3) (S4) 681.7 ab 7.4 a 0.350 a 17.36 a 62.68 b 0.27 a 666.0 b 8.0 a 0.326 a 17.05 a 66.65 b 0.25 a In a genotype, means labelled with different letters are different at P = 0.05. Table 3. Seed yield and yield components of canola cvs Karoo and Monty, and mustard line JN25 under rain-fed or irrigated conditions in the 2003 season Rain-fed (A) Irrigated (B) A/B Rain-fed (A) Irrigated (B) Seed yield (g/m 2 ) Seed no. (m 2 ) Karoo 164 bc 179 b 0.91 56652 a 57850 a 0.98 Monty 143 c 206 a 0.69 42627 b 53275 a 0.80 JN25 142 bc 161 bc 0.88 53498 a 54892 a 0.97 Statistical: Water Genotype W x G Water A/B Genotype W x G 100-seed wt (g) Harvest index Karoo 0.283 0.316 0.89 0.27 a 0.29 a 0.93 Monty 0.336 0.389 0.86 0.23 b 0.30 a 0.77 JN25 0.264 0.296 0.89 0.20 b 0.22 b 0.91 Statistical: Water Genotype W x G Water Genotype W x G For the main effects, P 0.05 and P 0.01. For the significant interactions, means of factorial treatments are labelled with different letters (P 0.05 ). Reference Ma, Q., Turner, D.W., Cowling, W.A., Levy, D. (2004). Searching for physiological markers that indicate drought tolerance in Brassica oilseeds. 2004 Agribusiness Crop Updates. Niknam, S.R., Ma, Q., Turner, D.W. (2003). Osmotic adjustment and seed yield of Brassica napus and B. juncea genotypes in a water-limited environment in south-western Australia. Australian Journal of Experimental Agriculture 43, 1127-1135. Richards, R.A., Thurling, N. (1978). Variation between and within species of rapeseed (Brassica campestris and B. napus) in response to drought stress. I. Sensitivity at different stages of development. Australian Journal of Agricultural Research 29, 469-477. Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994. Disclaimer
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